• Mario Kofler, Maxime Gaasch, Verena Rass, Alois J Schiefecker, Bogdan Ianosi, Anna Lindner, Ronny Beer, John F Stover, Paul Rhomberg, Bettina Pfausler, Claudius Thomé, Erich Schmutzhard, and Raimund Helbok.
• Neurological Intensive Care Unit, Department of Neurology, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria.
• Neurocrit Care. 2020 Feb 1; 32 (1): 135-144.

BackgroundThere is no uniform definition for cerebral microdialysis (CMD) probe location with respect to focal brain lesions, and the impact of CMD-probe location on measured molecule concentrations is unclear.MethodsWe retrospectively analyzed data of 51 consecutive subarachnoid hemorrhage patients with CMD-monitoring between 2010 and 2016 included in a prospective observational cohort study. Microdialysis probe location was assessed on all brain computed tomography (CT) scans performed during CMD-monitoring and defined as perilesional in the presence of a focal hypodense or hyperdense lesion within a 1-cm radius of the gold tip of the CMD-probe, or otherwise as normal-appearing brain tissue.ResultsProbe location was detected in normal-appearing brain tissue on 53/143 (37%) and in perilesional location on 90/143 (63%) CT scans. In the perilesional area, CMD-glucose levels were lower (p = 0.003), whereas CMD-lactate (p = 0.002), CMD-lactate-to-pyruvate-ratio (LPR; p < 0.001), CMD-glutamate (p = 0.002), and CMD-glycerol levels (p < 0.001) were higher. Neuroglucopenia (CMD-glucose < 0.7 mmol/l, p = 0.002), metabolic distress (p = 0.002), and mitochondrial dysfunction (p = 0.005) were more common in perilesional compared to normal-appearing brain tissue. Development of new lesions in the proximity of the CMD-probe (n = 13) was associated with a decrease in CMD-glucose levels, evidence of neuroglucopenia, metabolic distress, as well as increasing CMD-glutamate and CMD-glycerol levels. Neuroglucopenia was associated with poor outcome independent of probe location, whereas elevated CMD-lactate, CMD-LPR, CMD-glutamate, and CMD-glycerol levels were only predictive of poor outcome in normal-appearing brain tissue.ConclusionsFocal brain lesions significantly impact on concentrations of brain metabolites assessed by CMD. With the exception of CMD-glucose, the prognostic value of CMD-derived parameters seems to be higher when assessed in normal-appearing brain tissue. CMD was sensitive to detect the development of new focal lesions in vicinity to the neuromonitoring probe. Probe location should be described in the research reporting brain metabolic changes measured by CMD and integrated in statistical models.

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